Despite what someone mentioned below about incompatibility with OS X 10.3, this utility worked well with OS X 10.4. I was able to split a 386.4-MB text file into ten segments that were then separately openable by a wordprocessor, which I used to save them each in RTF. MS Word couldn't save a file a third of that size, even without any changes having been made to the plain text.

Thanks to this utility, I now have access to all the data on my "Infobases Collectors Library ’97 for Macintosh" CD-ROM on my MacBook Pro, which obviously cannot use Classic (Mac OS 9) to open the massive text library with the original pre-OS X application.